


The missing piece

by MarauderGirl



Category: Haikyuu!!
Genre: Alpha Miya Osamu, Alpha/Beta/Omega Dynamics, Anal Sex, Cum Eating, Cumming on Face, Incest, Knotting, M/M, Masturbation, Mating Bites, Mating Cycles/In Heat, Mentioned Komori Motoya/Sakusa Kiyoomi, Mis weas 💕, Multiple Orgasms, Omega Miya Atsumu, Rimming, Scent Kink, Separated at Birth, Sibling Incest, TsumuSamu (Day 4), TsumuSamu2020, Twincest, minor bleeding, someday i'll learn how to write pretty
Language: English
Status: Completed
Published: 2020-12-03
Updated: 2020-12-03
Packaged: 2021-03-10 01:01:37
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,342
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27835696
Author URL: https://archiveofourown.org/users/MarauderGirl/pseuds/MarauderGirl
Summary: Osamu just wanted to celebrate with a drink or two... He never expected to find a doppelganger in the process.
Relationships: Miya Atsumu/Miya Osamu
Comments: 26
Kudos: 242





	The missing piece

**Author's Note:**

> Miyacest Week 2020 (TsumuSamu2020)  
> Day 5 - Separated at Birth ( + ABO)
> 
> A really, really late entry… I’m sorry
> 
> I would say this is pretty vanilla for an ABO fic… but y’all be the judge. When the context is sex related, I never know with certainty if the content I come up with is too much or too little.
> 
> This was kindly beta read by [bakuguito](https://archiveofourown.org/users/bakuguito/pseuds/bakuguito) 💖

Osamu just wanted to celebrate, and get drunk.

He had just gotten out of a meeting with a possible investor for his small restaurant idea. A meeting that had gone excellent. This was their third meeting. The investor, an ex food critic, had asked for food samples, and had been delighted. He even gave him some tips to enhance the flavors of some of his onigiri. In that meeting, they came to an agreement and made plans to make a formal contract. This way Osamu would be able to start working on his dream restaurant as soon as possible.

He was elated and wanted to celebrate this achievement with his friends. He tried to make a small gathering, but sadly, everyone was busy. So they decided to meet on a later date for a proper celebration.

Even so, Osamu wanted to go out. It didn't matter that he was alone.

He decided on a small bar, where he could have some drinks, and maybe meet someone new. Despite not being as crowded as others he had seen, it was still pretty packed. After a couple of drinks, he was ready to try his social skills. The music was deafening, and he felt a bit fuzzy from the drinks. The drinks make his control a little loose, and without meaning he released some of his pheromones. He was looking around when he saw him. A blonde just turning his way and looking at him directly. A blond that was a carbon copy of him. A similar build, and the same face.

He looked as dumbstruck as he felt.

Without losing eye contact, instinctively, Osamu walks in his direction. He feels as if he needs to be by his side right now. As he approaches the still dumbstruck blonde, it hits him. A scent. A rich scent of peaches and ginger with a sweet lingering note. It feels like home. A home that he can’t place, but that makes him feel nostalgic.

It felt like he just found a piece of him that was missing.

That scent was definitely from an omega, and it came from the blonde. He was an omega. And not only that, he was an omega which scent he could pinpoint in a crowded bar. Usually, to perceive an omega's scent, he needs to be at least 2 meters closer. He shouldn't be able to smell him, but he can. As he breathed in the scent, he could feel getting drunker on it.

He sees the moment the blonde comes to the same realization. That even if they look the same, they are the opposite dynamic.

Osamu closes the distance between them. He can feel himself getting hotter and hotter as those omega pheromones get stronger.

~

Atsumu feels stuck in place.

He was minding his business, when he _smelled_ the best fucking alpha pheromones of all his life. He turns around, looking for the owner, and is met with... himself? A dark haired version. Looking directly at him.

He freezes up. He doesn’t understand what’s happening. How can this person exist? and why… Why is he the source of the pheromones?

The unknown alpha starts walking towards him, and he wants to move, but can't. He forces his body to relax, and suddenly being freezed up is no longer a problem. He feels hot. Too Hot. He knows this sensation, this feverish feeling, and… and he can feel slick pouring out of him.

This alpha, this doppelganger, triggered his heat.

He doesn't know what to do. He needs to leave now, but… he strongly wants to talk to the alpha. He feels wet heat slowly going down his thigh. He needs to leave now, before anyone else notices the fucking omega in heat. As his survival instincts quick in, he runs to the exit and hopes he can get a taxi to drive him home.

As he runs, he palms his pockets for his emergency suppressor. He can't find it. He remembers all the times his friends chastised him for not carrying it around. And swears at his overconfident pastself.

When he is finally outside the bar, the less crowded space makes him feel a bit safer. Unless people got closer, most wouldn’t be able to tell that his heat started. He takes the first taxi he can get, and finally relaxes in the smaller space…

As he closes the door, someone else pulls hard and opens it. Said person then pushes him lightly and sits beside him.

"I'm extremely sorry dear customer, but as you can see this young man got in fi-..." The driver, a beta man, says apologetically, until he turns around and sees both passengers. "Oh! never mind, I didn't notice you were together. Where should I drive you to?”. Atsumu hears static. The alpha followed him, and what's worse (He thinks?), it seems the driver believes they are related…

He still isn’t lost in his heat, but he is bewildered. He didn’t expect the alpha to follow him, and again, he doesn’t know what to do. He sees the alpha move his mouth, but he can’t hear it. He feels a bit overwhelmed. The taxi starts moving and the alpha is looking at him. His pheromones don’t feel as strong as in the bar. They are a bit dulled and still affect him, but less effectively. He bites his lip hard, in an attempt to concentrate on what's happening.

“... since you didn’t answer when I asked, we are going to my place” The alpha says, and adds after a moment. “It’s only 10 minutes away”

"... 'key" answers Atsumu in a small voice. He wants to disappear. He feels too hot and is a minute away from shamelessly grinding his seat, or worse, attacking the alpha.

~

Osamu can smell how the pheromones get heavier and heavier as the taxi advances through the almost non-existent traffic. At the bar, before sprinting after the omega, he applied his emergency suppressor. He felt a push to follow the omega, but he knew he needed a clear mind to do so. Now, in close quarters, he is sure he made the right choice. Even if the smell does make him crazy horny, it isn't close to triggering his rut. At least for now.

Osamu takes his time to admire the omega. They really look alike, even with the different dynamic and the different hair dye. As he keeps looking, his mouth waters, the omega looks tantalizing. He blushes with his whole face and keeps panting lightly. It seems he's doing his best not to grind against the seats, by the little aborted hips movements.

"By the way, I'm Osamu, what's your name?" Osamu asks.

"ah?... mnn… Atsumu" He answers lost in thought, and after a moment as an afterthought he adds "please take care of me… I guess"

Osamu blinks at the introduction. He didn’t expect such a formal greeting, especially in their current situation. He stays quiet as the other man seems to be in deep thought.

Atsumu decides to ignore the alpha as best as he can. He needs to concentrate. This heat feels like one of the biggest and he doesn't have any suppressors with him. At least he's still coherent, even if, as minutes pass, he can feel getting drunker and drunker on the alpha's scent. _Osamu's scent_ , his mind provides. He looks at him, trying not to draw his attention. The suppressor he took is losing effect, which is weird, since those things usually last longer. He really wants to keep that line of thought, but he gets distracted by a drop of sweat. It formed in his temple, and slowly went from his face to his neck, and finally getting lost into his covered pecs. He feels his mouth dry. He moves his eyes from that area, and forces them onto the other’s face.

He really looks the same as him, they must be related… but even with that knowledge, he can't help but picture himself getting wrecked by him. He knows he is panting hard, and lightly grinding on the seat. He feels **so horny**. If he asks for help, will he be willing to help? even with a dulled scent, Atsumu can tell that he wants to fuck him. _He took an alpha suppressor._ He bites his lips, if he asks for help, it would be okay. _Thanks to the suppressor, he should be clear headed enough. Even if my pheromones excite him._

Just as Atsumu is making up his mind, the taxi stops.

"That'll be ¥---"

Osamu pays the driver, and gets out of the car. Atsumu follows him, and as his legs touch the floor, he collapses.

He can feel his face burn with shame. He can't stand up, his legs feel like jelly, and his pants feel soaked.

"Are you alright??"

"Yeah, yeah… I just… can't…"

Osamu offers his back to him. "Here, it’s a short walk"

Atsumu accepts.

As Osamu carries him, Atsumu decides he needs to ask right now, when he can still speak coherently.

“I drank very little alcohol and I still have all my mental faculties”

“Mmm?”

“Without my suppressors... I can't get through my heat alone” He says in a frank tone, then coarsely adds “and your scent is making everything worse...” His face feels hot. His whole body feels like he's on fire. He can feel his asshole twitch and get wetter. His pants are completely ruined.

“Oh!... Do you want me to help you through it?”

“Yes” Atsumu whispers.

“Mmm…” Osamu hums, and then adds “Are you sure? We might be blood related...”

“I kno- know” Atsumu's voice breaks as he speaks. He feels raw. He feels so vulnerable. Osamu is an alpha that he just met, but he can’t help it… He feels as he needs him. “but… my instincts are going nuts, I can’t… I don’t know why, but your smell is driving me crazy and… and… it feels like home” 

The last bit was said in a whisper, something that Osamu almost didn't catch.

“I understand”

~~~

"Would you like to take a shower first?" Osamu asks as they enter his apartment.

"Please, fuck me"

"All right"

Osamu takes the omega to his room. He undresses him, and leaves him naked in bed.

"I'm going to get some water and some food... be right back"

Osamu goes to his kitchen and fills a jar with water, adding some isotonic powdered juice. Then he searches for some snack bars he knows he has saved. After gathering everything, he goes back to his room and finds Atsumu curled up inside his bed.

Inspecting the room he can see some of his clothes scattered around. Some sticking out the bed, where Atsumu is. Clothes that weren’t there before. It takes him a bit to peace together where those clothes came from. _Ah… those are my dirty clothes... mmm… figures he looked for something that reeked of alpha._

He leaves the food and water on his nightstand, and proceeds to remove his own clothing. When he is completely naked, he tries to get rid of the covers, but is met with some resistance. He hears Atsumu whine.

"Hey, it's me," he says in a deadpan way.

He waits for any kind of response, but gets nothing besides some movement under the covers. At least he can tell he was heard. He tries to remove the sheets again, this time being successful. Before he can say or do anything, he gets hit with some awfully concentrated pheromones.

He can see Atsumu panting hard with a really big hard on, and a blush covering most of his body. Looking closely at his face, he can see some of his dirty underwear.

"Did you get yourself worked up with those?" Osamu asks with a small smirk. He doesn’t know if he finds it hot or extremely endearing.

"Aa~ah" Atsumu whimpers. Osamu can see his eyes are really glassy.

He sits on his bed, and proceeds to kiss him hard as a distraction. He carefully touches his nipples and feels him moan into the kiss. He doesn’t stop kissing and continues moving his hands, going lower and lower. He deliberately avoids touching his dick, and instead starts massaging his inner thighs. At the avoidance, he feels Atsumu whine into the kiss, and bites his tongue lightly.

After sometime, he stops the teasing, and finally touches his dick. He rubs the head with his palm, and tries to get all the precum he can into his hand. Then, as he keeps kissing him, he grasps his dick and goes downward applying just enough pressure. Atsumu moaning hard breaks the kiss as he comes. Osamu feels him convulse as he hugs him hard, moving his hips as if looking for more friction from Osamu’s hand.

After the after shocks seem to pass, Atsumu lowers himself into the pillows and looks up to Osamu with teary eyes. He seems to be trying to calm his breath, wanting to say something. He looks extremely good. Before he says anything. Osamu lowers his head and starts licking at his nipples. As if a switch was turned on, Atsumu starts moaning hard.

“Ahh, Ahh~” He cries in pleasure.

 _His nipples are quite sensitive._ Osamu thinks, as he keeps licking and nibbling. He caresses his pectorals with his cheek. They are soft and firm.

Once more, Osamu starts touching his thighs. Atsumu has nicer thighs than him, fuller and firmer. He thinks how he could easily get obsessed with them.

As he massages his legs, he sees that Atsumu is hard again, but he decides to avoid touching him there and going directly for his balls. He fondles them for a bit, and then goes lower. Caressing his taint as he bites a bit harder on his nipples. Atsumu gives a particular loud moan at that. His taint is soft and wet with slick. He hasn't even started touching him there, but the whole area is full of slick.

He stops nibbling his nipples and starts kissing his lips, lightly biting, as his fingers brush the omega’s entrance. Atsumu keeps making little noises as he is being touched.

Osamu presses a finger in and is met with no resistance. Everything is extremely soft and hot and wet. The smell of peaches and ginger are suffocating. He can almost taste it in the air... He **really** wants to taste it. Atsumu breaks the heavy kissing.

"Please, please… i need it.." he mutters with tears forming in his eyes

"Tell me what you need..." Osamu asks with a soft tone. He wants to taste him. He wants to mess him up. He wants to fuck him until he can only cry from pleasure. He wants to knott him. Cum inside and… and fill him with his seed. Only for him. But… He also needs him to want it. He needs him to need this as much as his own instincts are crying at him.

"I… I... don't know" He starts crying. "I-I just- something, anything… I want more" 

_Ahh. So cute~._

Osamu feels something in him break. He feels his pheromones surge. The dullness provided by the repressor is completely gone, and with it, he feels as if a dam has been broken.

He takes Atsumu by the legs, and brings him lower in the bed. Then he bends him over by bringing his legs up in the air, leaving his asshole in clear view. With his left arm, Osamu brings him closer grabbing him by his waist, and tries to keep him firmly in place. And with his right arm, he jerks him off. When he has Atsumu stable enough, he licks over his entrance. Finally tasting his slick.

He gets lost in the sweetness as he prods him up with his tongue. He’d never had a sweet tooth, but he thinks he could keep eating him out forever.

Atsumu pants heavily and moans in a small voice, trying to be as quiet as possible.

The position makes it harder to breath, his back hurts, and keeping his legs up gets harder and harder… but even with all the discomfort, he feels in heaven. He feels his pleasure build up as Osamu not only uses his tongue but starts to add fingers inside. All this while he keeps stimulating him with his right hand.

Suddenly, Osamu stops working with his mouth.

“Hey, you don’t have to be so quiet. **I want to hear you** ” Osamu says using his commanding tone at the end. He knows it’s risky to use it since he doesn’t know for sure if they will be compatible in that aspect. But his instincts tell him that Atsumu won’t comply otherwise.

“Fu~uuck” Atsumu exclaims as he hears the command, and starts moaning hard. “Ah~ Ah” He takes the command with no issues. No headache. No nausea or revulsion. No rejection in sight. Just a need to please.

_Fuck, we are so compatible._

Osamu smiles to himself, and keeps working him up. He can’t get enough of his flavor. It tastes heavenly, but he needs to let go, so he can really use his fingers. Using two, he goes deeper and searches for the perfect spot. It doesn’t take him long to find it, and is rewarded with an especially loud moan. He decides to be a bit mischievous, and as he strokes his prostate, he goes for the head of his dick. Teasing his slit and spreading the wetness found there. 

The reaction is immediate. Atsumu cries in pleasure and trembles with his whole body as he comes all over this face.

Osamu feels… he feels like he's losing his control. He feels restless. His rut is being triggered, but can’t find the energy to care. He has the most perfect omega with him, crying in pleasure at his leisure. They will be perfectly fine.

He lets his legs fall into the bed, but keeps them apart so he can keep moving his fingers inside. As he keeps stimulating Atsumu, he looks at the mess he made, and smiles. He moves closer, and licks the still warm cum from Atsumu's face.

Atsumu can finally breathe. Taking long puffs of air, and breathing in Osamu’s scent. A scent that drives him crazy… even if he just came, he can feel himself getting harder by it. It’s such a rich and musky scent. He knows he is a mess, he can still feel cum on his face, and drying cum on his body. He can also feel his bottom completely covered in slick.

Osamu is so hard. It would be so easy to claim him. To just penetrate him and take his pleasure. He kisses him hard, and removes his fingers. He positionates their dicks together and grinds against him.

After sometime, Osamu breaks the kiss and asks. “Should I keep going? I could just use my mouth and fingers”

Atsumu looks lost, his gaze seems clearer than when they started. When he finally seems to process the words, his blush gets darker, but he smirks confidently as he grabs Osamu's cock in his hand. Getting closer to his face.

“I want this inside me” He says cockly.

He then grabs lower. Squeezing his uninflated knot, and adding "Specifically **this** "

Again a dam breaks inside Osamu. He grabs Atsumu, and turns him around. He manhandles him so his ass is on the air, and gives him a playful slap.

“You are a really bad boy, ye know?”

Atsumu wines at the smack, turns his face around and playfully says “So I've been told”

Osamu positionates himself, and in one movement penetrates Atsumu.

It’s like a switch turned on. He completely loses all the composure he had up until that moment. He loses himself onto his rut.

He sets a brutal pace with each movement hitting Atsumu just right. He is so wet that more than once he slips out, momentarily losing their rhythm. But just as easily as he slips, he resumes his brutish pace. He doesn’t know which of them is releasing more pheromones. He just knows that as their coupling goes on, their scents get intermingled. Something that pleases him immensely.

After sometime, he can feel his knot growing, enough that he no longer can keep the same pace as he fucks him deeply. Atsumu’s voice is a bit rough from moaning so much. A thing which makes him want him even more. He strongly wants to kiss him, but this position in particular makes it difficult. So he unilaterally decides to change it.

He removes himself from Atsumu, eliciting some complaints as he again grabs him forcefully and turns him around.

Now with his back to the bed he opens his legs and finds the best position to penetrate him. This time, he doesn’t bother trying to find a rhythm at first. He slowly pushes and pushes, until his knot finally catches. He swallows Atsumu cries of discomfort as he kisses him deeply. He waits for him to accommodate, and then… he starts to move his hips lightly, he has some small room to move and tries his best to keep going ball’s deep. 

He breaks the kiss, and goes for Atsumu’s scent gland. He licks and sucks at it, waiting for Atsumu to reject him or just to hit him. Instead of rejection he is met with acceptance, as Atsumu presents him with his neck giving him easier access. Osamu feels euphoric, and not only keeps licking but starts lightly biting at it.

He keeps grinding and moving until his knot reaches his limit as he comes.

Not really thinking about it he bites hard on his gland, drawing blood and cry of pain. Osamu hears himself moan as he tastes blood.

He feels his stomach warm and sticky from all the times Atsumu came between them. He then starts rubbing his own neck at Atsumu’s unharmed one, scenting the omega.

As time passes Atsumu gains more coherency, and pushes him lightly up. Then he buries his face onto Osamu’s neck and mutters “My turn” Osamu feels a bit puzzled at that, until he feels a sharp pain in his neck.

Atsumu bit him… on his scent gland… Atsumu just made them mates.

Connected as they are, still feeling pleasure from their physical connection, he feels overwhelmed… they just met, and now they are mates for life. He looks at Atsumu’s face astonished, he sees him get blurry. He blinks, and feels tears running down his face as Atsumu comes into focus.

He should be upset. He should be worried. He should be freaking out. But in his life, he can’t… It just feels right. He just feels love.

He sees Atsumu also start crying, but mixed with a light chuckle.

“Stupid… stop been a cry baby… you’re making me emotional” Atsumu chastises him.

“Sorry” He replies with a big smile, as he brings their foreheads together.

“Tsk…” He says as he starts to clench Osamu’s length.

“Ah~!” Osamu exclaims at the new stimulation. He is still buried deep inside Atsumu, and can feel his knot deflating…

“Come on… the fun just started” Atsumu says as he starts moving his hips up and down, clenching and unclenching, and setting a light pace. “We’ll talk later”

He grabs his head, lowering him into a passionate kiss, and biting his lip hard enough to bruise.

“Hey!” Osamu whimpers.

“Come on, I want you to put your back into it… We got all night long”

~~~

They wake up at 7pm the next day.

Osamu wakes up first and assesses the situation. The sheets are disgusting, beyond salvation. Dry cum, slick and blood everywhere. He doesn't remember much after they bonded, but he feels content. Again, he gets hit by that feeling as if a missing piece of himself is finally with him.

"Well, this might be difficult to explain" He mutters to no one in particular as he thinks of his mom, and what she'll probably say.

He watches Atsumu’s sleeping face, as he studies his features he comes to the conclusion that not only they must be related, but possibly twins. How could his mother never tell him about a twin? as hard as he tries, he can’t come up with a plausible reason.

After a while Atsumu wakes up, he yawns loudly and stretches his whole body. He doesn’t rise up or open his eyes, but slowly moves his hand to his neck, lightly touching it. It takes Osamu a while to get it. Atsumu is touching his mark. He must be remembering everything, how both bit each other and now are mates.

"Shit" Atsumu mutters. 

"You alright?"

"..." Atsumu doesn't want to answer, but he feels Osamu’s gaze as if expecting a reply. "... I play at volleyball's division 1… my team would want to meet my bondmate"

Osamu arches a brow expectantly "...and?"

"They’re gonna notice I bonded my relative? brother?… fuck Omi-kun will not let me live it down, specially after all the teasing I did"

"Omi-kun? teasing?" Osamu asks, a bit confused.

"He mated his cousin… and I teased him about how he always trashed alphas” He replies, and then adds with a light blush on his face“... but that keeping it in the family was his deal"

Osamu gazes at him with a look of silent judgement. "You're the worst"

"Hey!" Atsumu exclaims indignantly. “I wasn’t mean about it… It just was fun seeing him get flustered at the mention of Komori-kun”

Osamu sights. 

“Don’t worry… I’ll be right beside you the whole time”

Atsumu feels his face getting hotter.

“I’ll even hold your hand” He adds teasingly.

“Stupid-samu”

“Come on, you must be hungry… I’ll prepare you the future star dishes from Onigiri Miya, trademark pending”

As Atsumu looks at Osamu’s smile. He thinks that everything will be alright, because everything seems to be just in the right place. And even if he doesn’t know what the future might convey, they’ll be together against the world.

~fin~

**Author's Note:**

> Ok… look, I’ve been reading ABO since the shit came to fruition on the kink meme prompts and I really enjoy seeing it evolve, and love how, since it’s a fandom trope, everyone comes up with their own AUs and ideas... for example: I love how the japanese BL mangakas took it, added the ‘fated pair’ concept, and have been having fun with the trope. I don’t believe in the “right kind of ABO” fics that I’ve seen some people talk about, each kink/trope used has their own demographic, if you didn’t like some shit, then it wasn’t for you… I don’t understand why some people try to bring fandom policing on a trope that inherently started as a “horny&kinky as fuck” prompt.
> 
> Here I’m writing **my** kind of ABO trope, with elements that I’ll possibly use in any future ABO fics I write… :)
> 
> On a lighter note, I’ll tell you something funny that happened when I was trying to come up with Atsumu’s scent… I wanted Atsumu’s scent to be something typical from their region, but everything I found was like some meat-based dish… and got me going like: “oh yes… atsumu’s scent was so delicious… he smelled just like Kobe beef steak/Beef cutlet”... so~ sexy 😂💕
> 
> I tried my best… and as always, any constructive criticism is welcome.


End file.
